Chemical potential of quasi-equilibrium magnon gas driven by pure spin current

TL;DR

This paper experimentally demonstrates that pure spin currents can induce a quasi-equilibrium magnon gas in a ferromagnet, characterized by Bose-Einstein statistics, with potential for spin current-driven Bose-Einstein condensation.

Contribution

It provides the first experimental evidence that spin Hall effect-generated spin currents can control magnon populations and induce conditions akin to Bose-Einstein condensation.

Findings

Magnon gas reaches quasi-equilibrium state under spin current

Chemical potential approaches magnon ground state at high currents

Magnon population follows Bose-Einstein statistics

Abstract

We show experimentally that the spin current generated by the spin Hall effect drives the magnon gas in a ferromagnet into a quasi-equilibrium state that can be described by the Bose-Einstein statistics. The magnon population function is characterized either by an increased effective chemical potential or by a reduced effective temperature, depending on the spin current polarization. In the former case, the chemical potential can closely approach, at large driving currents, the lowest-energy magnon state, indicating the possibility of spin current-driven Bose-Einstein condensation.